Yogeshwar Mishra

Reliable LIF/Mie droplet sizing in sprays using structured laser illumination planar imaging

In this article, Structured Laser Illumination Planar Imaging (SLIPI) is used in combination with the LIF/Mie ratio technique for extracting a reliable two-dimensional mapping of the droplets Sauter Mean Diameter (SMD). We show that even for the case of a fairly dilute spray, where single scattering events are in majority, the conventional LIF/Mie technique still remains largely affected by errors introduced by multiple light scattering. To remove this unwanted light intensity on both the LIF and Mie images SLIPI is used prior to apply the image ratio. For the first time, the SLIPI LIF/Mie results are calibrated and compared with measurement data from Phase Doppler Interferometry (PDI).

Thermometry in aqueous solutions and sprays using two-color LIF and structured illumination

In imaging, the detection of light originating from multiple scattering, indirect reflections and surrounding backgrounds are known to produce errors especially in intensity-ratio based measurements. SLIPI (Structured Laser Illumination Planar Imaging) is an imaging technique that significantly reduces the impact of such issues. In this study, SLIPI is combined with the two-color LIF (Laser Induced Fluorescence) ratio thermometry approach for measuring water temperature in both a cuvette and a hollow-cone spray. By removing the unwanted background interferences using SLIPI, we observe both significant improvements in terms of temperature sensitivity as well as more pronounced temperature gradients within the spray.

Analysis of ethanol and butanol direct-injection spark-ignition sprays using two-phase structured laser illumination planar imaging droplet sizing

This paper reports on the spray structure of the biofuels, ethanol, and butanol generated by a multihole direct-injection spark-ignition injector, which is studied in a constant volume chamber. The spray shape and structure are analyzed using two-phase structured laser illumination planar imaging where both laser-induced fluorescence and Mie-scattering light are recorded simultaneously for the extraction of instantaneous laser-induced fluorescence/Mie-scattering ratio images. Quantitative planar measurements of the droplet Sauter mean diameter are conducted, using calibration data from phase-Doppler anemometry. The resulting Sauter mean diameters are presented for ethanol and butanol at various fuel temperatures at different times after the start of injection. It is found that an increase in fuel temperature results in a faster atomization and higher evaporation rate, which leads to reduced spray tip penetration and smaller droplet Sauter mean diameter. At equivalent conditions, butanol consistently showed larger spray tip penetration in comparison to ethanol. This behavior is due to the higher surface tension and viscosity of butanol resulting in the formation of larger droplets and larger Sauter mean diameters in the whole spray region. Finally, the butanol injection also shows larger cyclic variations in the spray shape from injection to injection which is explained by the internal nozzle flow that is influenced by larger fuel viscosity as well. The Sauter mean diameter distribution is also compared to phase-Doppler anemometry data showing good agreement and an uncertainty analysis of the structured laser illumination planar imaging-laser-induced fluorescence/Mie-scattering technique for planar droplet sizing in direct-injection spark-ignition sprays is presented.